In canola as well as other crops, various fungal and insect diseases exist that are manifested in the roots of the plant. Although the plant's roots are underground, conventional methods of treatment to prevent or control root diseases come from above ground. These conventional treatments include the application of a variety of chemicals via sprays, granules and the like. These conventional treatments are both labor intensive and costly. Often, the exposed edible portion of the crop plant receives application of the chemical agent that is intended for localization at the roots. On occasion, the conventional treatments require that the applied chemical agent be worked into the ground. However, care must be exercised to avoid damaging the plant's roots. Because conventional treatments are applied from above ground, excess quantities of the chemical agent must be applied to maintain an effective concentration at the portion of the root zone furthest from the application point.
It is an object of the present invention to provide a means for generally or specifically conferring immunity or resistance to fungal or insect diseases on a plant whose roots are susceptible to such a disease.
It is a further object of the present invention to provide the components and a method for conferring disease resistance on the roots of food crops that eliminates conventional treatments and that exhibits minimal or no manifestation in the edible fruit or leafy portions of the plant.
The process of tissue and organ development in plants involves the temporal and spatial expression of a large array of genes that determine the patterns of cell division, elongation and differentiation leading to the final structure and function of the tissue or organ. For example, Kamalay and Goldberg (Cell 19:935, 1980; Proc. Natl. Acad. Sci. USA, 81:2801, 1984) estimated that as many as 25,000 diverse genes may be expressed in the tobacco anther. Of these, as many as 10,000 are anther-specific. While these many genes may not be unique to every organ, many tissue types from several species have been studied to date, and have revealed sets of genes which appear to be either uniquely, or predominantly expressed in individual tissues.
The identification and isolation of genes associated with tissue-specific expression in Brassica species has been less prevalent, but several genes exhibiting tissue- or stage-dependent expression have been isolated and characterized. These include genes unique to or abundant in seed (Simon et al., Plant Mol. Biol. 5:191, 1985; Scofield and Crouch, J. Biol. Chem. 262:12202, 1987; Baszczynski and Fallis, Plant Mol. Biol. 14:633, 1990); leaf (Baszczynski et al., Nuc. Acids Res. 16:4732, 1988; Boivin et al., in preparation); stigma (Nasrallah et al., Proc. Natl. Acad. Sci. USA 85:5551, 1988; Trick, Plant Mol. Biol. 15:203, 1990), microspore and pollen (Albani et al., Plant Mol. Biol. 15:605, 1990; Albani et al., Plant Mol. Biol. 16:501, 1991); and recently, root (Fallis and Baszczynski unpublished; Bergeron et al., in preparation). In the last several years, promoters have been fused to reporter or other agronomic genes for molecular transformation, and the degree and specificity of expression has been measured. Examples include Stockhaus et al. (Proc. Natl. Acad. Sci. USA 85:7943, 1987); An et al. (Plant Physiol. 88:547, 1988); Ellis et al. (Plant Mol. Biol. 10:203, 1988); Guerrero et al. (Mol. Gen. Genet. 224:161, 1990); Ohl et al. (Cell 2:837, 1990); van der Meer et al. (Plant Mol. Biol. 15:95, 1990); Vorst et al. (Plant Mol. Biol. 14:491, 1990); Baszczynski et al. (Proc. 3rd ISPMB Internat. Congr., Tucson, Arizona, abstr. 430, 1991); Takaiwa et al. (Plant Mol. Biol. 16:49, 1991); van der Zaal at al. (Plant Mol. Biol. 16:983, 1991).
Several reports have described sequences which direct expression of genes either predominantly in root tissues, or which express in various tissues including roots (Tingey et al., EMBO J. 6:1, 1987; An et al., Plant Physiol. 88:547, 1988; Oppenheimer et al., Gene 63:87, 1988; Conkling et al., Plant Physiol. 93:1203, 1990; Ohl et al., Cell 2:837, 1990; van der Zaal et al., Plant Mol. Biol. 16:983, 1991).
U.S. Pat. No. 4,803,165 (Applebaum) teaches the transformation of the nitrogen fixing organism, Rhizobium japonicum, to express the toxic crystal protein of Bacillus thuringiensis under control of the nif promoter of R. japonicum. U.S. Pat. No. 5,008,194 (Rolfe et al.) further teaches the transformation of Bradyrhizobium japonicum, to express the toxic crystal protein of Bacillus thuringiensis under control of the nifH promoter of B. japonicum. Because the transformed nitrogen fixing bacteria of Applebaum and Rolfe have symbiotic relationships that are confined in nature to the root nodules of the leguminous plants, Applebaum and Rolfe have no applicability to the non-leguminous plants of the world. Further, both Applebaum and Rolfe transform a symbiotic organism and not the plant itself. Accordingly, the seeds of the leguminous plants that were infected with the transformed organism are incapable of carrying the gene expressed by a bacterium in the root nodules of the parent plant. Thus, to utilize the inventions of Applebaum or Rolfe, purchasers of leguminous seed would also be required to purchase an appropriate transformed nitrogen fixing organism to infect their soils.
It is an object of the present invention to provide a means for conferring immunity or resistance to disease on any plant root that is susceptible to disease.
It is also an object of the present invention that the tract of immunity or resistance to a root disease be carried in the seeds of each succeeding generation of plant.